Nowadays, plastic components play an essential role in many areas of technology and everyday life. As examples, the aviation and aerospace industry as well as the automotive industry are mentioned. In these areas, plastic components may, for example, serve as impact protection elements, e.g. bumpers, or they may be used for the manufacture of panel-elements, seat shells, arm rests, and so forth. Plastic components may also be used in the packing industry, for example, for packing up sensitive and easily damaged goods for delivery.
In all of these exemplary areas of application, it is desirable that the plastic components comprise as small a weight as possible, being, however, at the same time sufficiently resilient. In particular, with regard to plastic components being used for impact protection or for safely wrapping up goods, plastic components should also comprise good cushioning and absorption properties with regard to blows or hits. In this context, foamed plastic materials are known, like for example expanded polystyrene—e.g. available from BASF under the trade names of Styropor® or Styrodur®.
The use of expanded plastic materials has also found its way into the manufacture of cushioning elements for sports apparel, for example for the manufacture of shoe soles for sports shoes. In particular, the use of particles of expanded thermoplastic polyurethane (eTPU), which are fused together by supplying heat in the form of steam or connected by the use of a binder material as described in DE 10 2012 206 094 A1 and DE 10 2011 108 744 B1, was considered. The use of particles from eTPU has turned out to be beneficial in order to provide shoe soles or parts of soles with a low weight, good temperature stability and small hysteresis-losses with regard to the energy exerted for the deformation of the sole during running.
In addition, DE 10 2013 002 519 A1 discloses extended possibilities for the manufacture of cushioning elements for sports apparel from such particles, for example by loading a mold with the particles via a stream of liquid or steam.
Common to the methods known is, however, that the processing of the base material to dimensionally stable components of a high quality is often only possible up to a certain thickness or a certain packing density, meaning that the possible shapes of components that may be manufactured may be limited. This is due to the fact that the known manufacturing methods necessitate supplying the binder material or heat energy also to the interior of the components. For a liquid binder material or heat energy supplied by steam, this is only possible to a limited degree for thicker components and/or may lead to imperfections, because “channels” or “inlet openings” are provided in the component to allow the binder or the steam to homogeneously infuse the base material within the mold. Moreover, in particular when using steam as an energy carrier, it turns out to be undesirable that a major share of the energy stored within the steam may be lost in the mold instead of being supplied to the particles/particle surfaces. This may, on the one hand, necessitate a long pre-heating phase until the mold is heated up to a saturation temperature, and may, on the other hand, delay stabilization and cooling of the fused component since the mold may have stored a large amount of heat energy that delays cooling. Therefore, the method may be protracted and very energy inefficient.
It is therefore an objective underlying the present invention to provide improved methods for the manufacture of plastic components, in particular of cushioning elements for sports apparel, which allow the manufacture of complexly shaped plastic components with potentially greater thickness and packing densities, without significantly compromising the quality of the finished components. Furthermore, the manufacturing effort shall be kept low and the manufacturing and cooling duration short, and the method shall further be as energy efficient as possible while making do without poisonous or environmentally hazardous substances.